Magnetic implants with improved anatomical compatibility

ABSTRACT

A distraction system includes a first distraction device having a first adjustable portion and a first distraction rod configured to telescope within the first adjustable portion, the first adjustable portion having contained therein a first rotatable magnetic assembly mechanically coupled to a first screw configured to axially telescope the first distraction rod. A second distraction device is provided and includes a second adjustable portion and a second distraction rod configured to telescope within the second adjustable portion, the second adjustable portion having contained therein a second rotatable magnetic assembly mechanically coupled to a second screw configured to axially telescope the second distraction rod. An adjustable joint connects one end of the first adjustable portion to one end of the second adjustable portion.

FIELD OF THE INVENTION

The field of the invention generally relates to medical devices fortreating disorders of the skeletal system.

BACKGROUND

Scoliosis is a general term for the sideways (lateral) curving of thespine, usually in the thoracic or thoracolumbar region. Often, there isalso a rotation of the spine as well as curvature. Scoliosis is commonlybroken up into different treatment groups, Adolescent IdiopathicScoliosis, Early Onset Scoliosis and Adult Scoliosis.

Adolescent Idiopathic Scoliosis (AIS) typically affects children betweenages 10 and 16, and becomes most severe during growth spurts that occuras the body is developing. One to two percent of children between ages10 and 16 have some amount of scoliosis. Of every 1000 children, two tofive develop curves that are serious enough to require treatment. Thedegree of scoliosis is typically described by the Cobb angle, which isdetermined, usually from x-ray images, by taking the most tiltedvertebrae above and below the apex of the curved portion and measuringthe angle between intersecting lines drawn perpendicular to the top ofthe top vertebrae and the bottom of the bottom. The term idiopathicrefers to the fact that the exact cause of this curvature is unknown.Some have speculated that scoliosis occurs when, during rapid growthphases, the ligamentum flavum of the spine is too tight and hinderssymmetric growth of the spine. For example, as the anterior portion ofthe spine elongates faster than the posterior portion, the thoracicspine begins to straighten, until it curves laterally, often with anaccompanying rotation. In more severe cases, this rotation actuallycreates a noticeable deformity, wherein one shoulder is lower than theother. Currently, many school districts perform external visualassessment of spines, for example in all fifth grade students. For thosestudents in whom an “S” shape or “C” shape is identified, instead of an“I” shape, a recommendation is given to have the spine examined by aphysician, and commonly followed-up with periodic spinal x-rays.

Typically, patients with a Cobb angle of 20° or less are not treated,but are continually followed up, often with subsequent x-rays. Patientswith a Cobb angle of 40° or greater are usually recommended for fusionsurgery. It should be noted that many patients do not receive thisspinal assessment, for numerous reasons. Many school districts do notperform this assessment, and many children do not regularly visit aphysician, so often, the curve progresses rapidly and severely. In AIS,the ratio of females to males for curves under 10° is about one to one,however, at angles above 30°, females outnumber males by as much aseight to one. Fusion surgery can be performed on the AIS patients or onadult scoliosis patients. In a typical posterior fusion surgery, anincision is made down the length of the back and Titanium or stainlesssteel straightening rods are placed along the curved portion. These rodsare typically secured to the vertebral bodies, for example with bonescrews, or more specifically pedicle screws, in a manner that allows thespine to be straightened. Usually, at the section desired for fusion,the intervertebral disks are removed and bone graft material is placedto create the fusion. If this is autologous material, the bone isharvested from a hip via a separate incision.

Alternatively, the fusion surgery may be performed anteriorly. A lateraland anterior incision is made for access. Usually, one of the lungs isdeflated in order to allow access to the spine from this anteriorapproach. In a less-invasive version of the anterior procedure, insteadof the single long incision, approximately five incisions, each aboutthree to four cm long are made in several of the intercostal spaces(between the ribs) on one side of the patient. In one version of thisminimally invasive surgery, tethers and bone screws are placed and aresecured to the vertebra on the anterior convex portion of the curve.Currently, clinical trials are being performed which use staples inplace of the tether/screw combination. One advantage of this surgery incomparison with the posterior approach is that the scars from theincisions are not as dramatic, though they are still located in avisible area, when a bathing suit, for example, is worn. The stapleshave had some difficulty in the clinical trials. The staples tend topull out of the bone when a critical stress level is reached.

Commonly, after surgery, the patient will wear a brace for a few monthsas the fusing process occurs. Once the patient reaches spinal maturity,it is difficult to remove the rods and associated hardware in asubsequent surgery, because the fusion of the vertebra usuallyincorporates the rods themselves. Standard practice is to leave thisimplant in for life. With either of these two surgical methods, afterfusion, the patient's spine is now straight, but depending on how manyvertebra were fused, there are often limitations in the degree offlexibility, both in bending and twisting. As these fused patientsmature, the fused section can impart large stresses on the adjacentnon-fused vertebra, and often, other problems including pain can occurin these areas, sometimes necessitating further surgery. Many physiciansare now interested in fusionless surgery for scoliosis, which may beable to eliminate some of the drawbacks of fusion.

One group of patients in which the spine is especially dynamic is thesubset known as Early Onset Scoliosis (EOS), which typically occurs inchildren before the age of five. This is a more rare condition,occurring in only about one or two out of 10,000 children, but can besevere, sometimes affecting the normal development of organs. Because ofthe fact that the spines of these children will still grow a largeamount after treatment, non-fusion distraction devices known as growingrods and a device known as the VEPTR—Vertical Expandable ProstheticTitanium Rib (“Titanium Rib”) have been developed. These devices aretypically adjusted approximately every six months, to match the child'sgrowth, until the child is at least eight years old, sometimes untilthey are 15 years old. Each adjustment requires a surgical incision toaccess the adjustable portion of the device. Because the patients mayreceive the device at an age as early as six months old, this treatmentrequires a large number of surgeries. Because of the multiple surgeries,these patients have a rather high preponderance of infection and othercomplications. A new magnetically controlled growing rod is now beingused which allows adjustments to be done non-invasively, as reported inthe article “Magnetically controlled growing rods for severe spinalcurvature in young children: a prospective case series”, Cheung et. al.,Lancet, 2012.

Returning to the AIS patients, the treatment methodology for those witha Cobb angle between 20° and 40° is quite controversial. Many physiciansprescribe a brace (for example, the Boston Brace), that the patient mustwear on their body and under their clothes 18 to 23 hours a day untilthey become skeletally mature, for example to age 16. Because thesepatients are all passing through their socially demanding adolescentyears, it is quite a serious prospect to be forced with the choice ofeither wearing a somewhat bulky brace that covers most of the upperbody, having fusion surgery that may leave large scars and also limitmotion, or doing nothing and running the risk of becoming disfigured andpossibly disabled. It is commonly known that many patients have at timeshidden their braces, for example, in a bush outside of school, in orderto escape any related embarrassment. The patient compliance with bracewearing has been so problematic, that there have been special bracesconstructed which sense the body of the patient, and keep track of theamount of time per day that the brace is worn. Patients have even beenknown to place objects into unworn braces of this type in order to foolthe sensor. Coupled with the inconsistent patient compliance with braceusage, is a feeling by many physicians that braces, even if usedproperly, are not at all effective at curing scoliosis. These physiciansmay agree that bracing can possibly slow down or even temporarily stopcurve (Cobb angle) progression, but they have noted that as soon as thetreatment period ends and the brace is no longer worn, often thescoliosis rapidly progresses, to a Cobb angle even more severe than itwas at the beginning of treatment. Some say the reason for the supposedineffectiveness of the brace is that it works only on a portion of thetorso, and not on the entire spine. Currently a 500 patient clinicaltrial known as BrAIST (Bracing in Adolescent Idiopathic Scoliosis Trial)is enrolling patients, 50% of whom will be treated with the brace and50% of who will simply be watched. The Cobb angle data will be measuredcontinually up until skeletal maturity, or until a Cobb angle of 50° isreached, at which time the patient will likely undergo surgery.

Though this trial began as a randomized trial, it has since been changedto a “preference” trial, wherein the patients choose which treatment armthey will be in. This is partially because so many patients wererejecting the brace. Many physicians feel that the BrAIST trial willshow that braces are completely ineffective. If this is the case, thequandary about what to do with AIS patients who have a Cobb angle ofbetween 20° and 40° will only become more pronounced. It should be notedthat the “20° to 40° ” patient population is as much as ten times largerthan the “40° and greater” patient population.

Currently, genetic scientists have found and continue to find multiplegenes that may predispose scoliosis. Though gene tests have beendeveloped, including a scoliosis score for risk of curve progression,some are still skeptical as to whether gene therapy would be possible toprevent scoliosis. However the existence of a scoliosis gene would nodoubt allow for easier and earlier identification of probable surgicalpatients.

Scoliosis is also present in patients with mature spines. One type ofmalady in mature patients is known as adult idiopathic scoliosis. Itshould be noted for reference purposes that the spine is actually maturein girls as young as fifteen or sixteen years old. In boys the maturityoften occurs at a slightly older age of about eighteen years. Adultidiopathic scoliosis should be differentiated from what is known as denovo scoliosis or degenerative scoliosis, and which is predominantlycaused by degeneration of the disc and facets with age., often combinedwith poor bone quality from osteopenia and osteoporosis. Oftentimes,fusion surgery in patients having mature spines with deformitiesrequires significantly invasive measures to straighten the spine. Thisincludes performing osteotomies (cutting out sections of the vertebrae)performed either from a posterior access or from an anterior access tothe spine. Some types of osteotomies include Smith-Peterson osteotomy(SPO), pedicle subtraction osteotomy (PSO), and vertebral columnresection (VCR). Because these osteotomies require more time and moreinvasive surgical techniques, their use adds significant cost andcomplications to fusion surgery.

There is a large population of mature spine patients with untreatedscoliosis, in extreme cases with a Cobb angle as high as or greater than60°, or even higher than 90°. In some cases, straightening this spineduring a single fusion surgery could be problematic, even causing severeneurological problems. Many of these adults, though, do not have painassociated with this deformity while untreated, and live relativelynormal lives, though oftentimes with restricted mobility and motion. Itis contemplated that the devices and methods described herein also haveapplication in the treatment of adult scoliosis. Adult scoliosis cancontinue to worsen with time. Though the adult is skeletally mature, theCobb angle may still continue to increase with time. The relaxation orslight reduction in height that occurs in adults may have some relationwith this increase in Cobb angle. Curves above 100° are rare, but theycan be life-threatening if the spine twists the body to the point wherepressure is put on the heart and lungs. The magnetically controlledgrowing rod has been described before as a treatment method of adultscoliosis, e.g., allowing adult scoliosis to be treated with a minimallyinvasive and/or fusionless approach. In addition, gradual adjustment ofthe spine may be desired, especially in the cases of very high Cobbangles. For example, it may be desired to limit the amount of stresseson the bones or on the implant materials, by first adjusting an adultscoliosis patient so that their Cobb angle is reduced 50% or less, then15% or less each few months, until the spine is straight. As oneexample, the initial surgical implantation may reduce the Cobb angle by50% or more by the physician performing manual distraction on the spine.Post-implantation, the Cobb angle can be reduced in a non-invasivemanner by application of a constant or periodically changing distractionforce. A first non-invasive adjustment may result in a Cobb anglereduction of less than 50%. Additional non-invasive adjustments may beperformed which result in even smaller Cobb angle reductions (e.g., lessthan 15% from original Cobb angle).

In this regard, the Cobb angle may be reduced by a smaller amount overthe next few months (e.g., less than around 15% each monthpost-operation). The non-invasive adjustment of a fusionless implantmade possible by the invention allows for a gradual adjustment scheme ofthis nature. Moreover, the distraction forces used over this period oftime are generally low (e.g., distraction force less than 45 pounds)which means, among other things, less patient discomfort, and lesschance of failure within the adjustable rods. Non-invasive adjustmentsmay be periodically performed when the patient visits his or herphysician. This may occur over a span of more than one week (e.g., aseveral week process). Of course, the number and periodicity of theadjustments is a function of, among other things, the Cobb angle of thepatient.

Oftentimes, the adult spine has less dense or even osteoporotic bone, soit may be desirable to combine the sort of gradual adjustment describedhere with additional methods to strengthen the bone, for example thebone of the vertebral bodies. One method is to strengthen the vertebralbody by performing prophylactic vertebroplasty or kyphoplasty, whereinthe internal area of the vertebral body is strengthened, for example byinjection of bone cement or Polymethyl Methacrylate (PMMA).Additionally, if pedicle screws are used for fixation, the surface ofthe screws may be treated with a biologic material that promotes bonegrowth, or a surface characteristic that improves bone adhesion. Any ofthese methods would further improve the possibilities that thedistraction forces would not cause fracture or other damage to thevertebrae of the patient.

In use, magnetically controlled growing rods are often cut and bent inthe desired curves prior to implantation in the patient. It is commonpractice then to test the magnetically controlled growing rodimmediately prior to placing in the patient (for example after cuttingand bending) to confirm that it is completely operational. This ofteninvolves placing a sterile cover over the external adjustment devicethat is used to lengthen the magnetically controlled growing rod. Thisadditional operation is not ideal because of the extra effort to bringthe external adjustment device into the operating room, the extra effortto maintain sterility, and the fact that the external adjustment devicecontains powerful magnets, which can attract structures of the surgicaltable as well as surgical instruments.

SUMMARY

In one embodiment, a distraction system includes a first distractiondevice having a first adjustable portion and a first distraction rodconfigured to telescope within the first adjustable portion, the firstadjustable portion having contained therein a first rotatable magneticassembly mechanically coupled to a first screw configured to axiallytelescope the first distraction rod. The system includes a seconddistraction device having a second adjustable portion and a seconddistraction rod configured to telescope within the second adjustableportion, the second adjustable portion having contained therein a secondrotatable magnetic assembly mechanically coupled to a second screwconfigured to axially telescope the second distraction rod. Thedistraction system includes an adjustable joint connecting one end ofthe first adjustable portion to one end of the second adjustableportion.

In another embodiment, a distraction system includes a first distractiondevice with a first adjustable portion having contained therein a firstrotatable magnetic assembly. The system includes a second distractiondevice with a second adjustable portion having contained therein asecond rotatable magnetic assembly; and a common distraction rod havingfirst and second opposing ends, wherein a first end of the commondistraction rod is mechanically coupled to the first rotatable magneticassembly and wherein a second end of the common distraction rod ismechanically coupled to the second rotatable magnetic assembly.

In yet another embodiment, a distraction system includes an adjustableportion having contained therein a rotatable magnetic assembly, theadjustable portion being at least one of curved or angled; and adistraction rod mechanically coupled to the rotatable magnetic assemblyvia a screw and configured for telescopic movement relative to theadjustable portion.

In still another embodiment, a distraction system includes an adjustableportion having contained therein a rotatable magnetic assembly; a screwoperatively coupled to the rotatable magnetic assembly; and adistraction rod having a recess formed therein, the recess containing anut having internal threads, the nut having first and second collaredends disposed on either side of the internal threads, wherein the screwinterfaces with the internal threads of the nut and wherein rotation ofthe rotatable magnetic assembly effectuates telescopic movement of thedistraction rod relative to the adjustable portion.

In another embodiment, a distraction system includes an adjustableportion having contained therein a rotatable magnetic assembly; adistraction rod mechanically coupled to the rotatable magnetic assemblyvia a screw and configured for telescopic movement relative to theadjustable portion; and a distraction tester including a body having acylindrical cavity passing through the body, wherein the distractiontester has a first circumferential portion of the body that has a highermass of magnetically permeable material than a second circumferentialportion, spaced apart from the first circumferential portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the spine of a person with scoliosis.

FIG. 2 illustrates the Cobb angle of a scoliotic spine.

FIG. 3 illustrates the small incisions made during scoliosis non-fusionsurgery of the inventive embodiments.

FIG. 4 illustrates an exemplary distraction device mounted on the spineof a subject.

FIG. 5 illustrates a perspective view of one end of a distraction rodillustrating the splined tip.

FIG. 6 is a side cross-sectional view of the tubular housing with thelead screw and magnetic assembly removed for clarity.

FIG. 7 is a cross-sectional view of the tubular housing taken along theline C′-C in FIG. 6.

FIG. 8 illustrates an embodiment of a distraction device having amaintenance member.

FIG. 9A illustrates a sectional view of the distraction device of FIG. 8taken along the line 9A-9A.

FIG. 9B illustrates a cross-sectional view of the distraction device ofFIG. 8 taken along the line 9B-9B.

FIG. 10 illustrates a cylindrical maintenance member from thedistraction device of FIGS. 8, 9A, and 9B.

FIG. 11 illustrates an external adjustment device that is used with thedistraction devices described herein.

FIG. 12 illustrates a distraction device having an angularly adjustable,lockable joint.

FIG. 13 illustrates a detailed view of the angularly adjustable,lockable joint of the distraction device of FIG. 12.

FIG. 14 illustrates a second detailed view of the angularly adjustable,lockable joint of the distraction device of FIG. 12.

FIG. 15 illustrates a distraction device having a bendable sectionbetween two actuators.

FIG. 16 illustrates a distraction device having an actuator with anangled shape.

FIG. 17A illustrates the internal drive structure of the distractiondevice of FIG. 16, incorporating a universal joint.

FIG. 17B illustrates a cross structure used as part of a universaljoint.

FIG. 17C illustrates an alternative magnetic assembly.

FIG. 18 illustrates a manual distraction tester.

FIG. 19 illustrates a manual distraction tester placed upon adistraction device.

FIG. 20 illustrates a manual distraction tester being turned in a firstdirection.

FIG. 21 illustrates a manual distraction tester being turned in a seconddirection.

FIG. 22 illustrates a distraction rod with an improved nut havingcollars.

FIG. 23 illustrates a detail of one end of the distraction rod of FIG.22.

FIG. 24 illustrates a longitudinal section of FIG. 23 taken along lines24-24.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a patient 100 with scoliosis. The concave portion 102of the spinal curve can be seen on the left side 104 of the patient 100,and the convex portion 106 can be seen on the right side 108 of thepatient 100. Of course, in other patients, the concave portion 102 mayappear on the right side 108 of the patient 100 while the convex portion106 may be found on the left side 104 of the patient. In addition, asseen in FIG. 1, some rotation of the spine 110 is present, andunevenness between the left shoulder 112 and right shoulder 114 is seen.

FIG. 2 illustrates the Cobb angle 116 of a spine 110 of a patient withscoliosis. To determine the Cobb angle, lines 118 and 120 are drawn fromvertebra 122 and 124, respectively. Intersecting perpendicular lines 126and 128 are drawn by creating 90° angles 130 and 132 from lines 118 and120. The angle 116 created from the crossing of the perpendicular lines126 and 128 is defined as the Cobb angle. In a perfectly straight spine,this angle is 0°.

In many Adolescent Idiopathic Scoliosis (AIS) patients with a Cobb angleof 40° or greater, spinal fusion surgery is typically the first option.Alternatively, non-fusion surgery may be performed, for example with thedistraction device 200 of FIG. 4. FIG. 3 illustrates an upper incision136 and a lower incision 138 formed in the patient 100 which istypically made during non-fusion scoliosis surgery.

FIG. 4 illustrates a distraction device 200 for treating scoliosisaccording to one embodiment of the invention. The distraction device200, which is an implantable device, is fixated at its upper end 202 andlower end 204 to the patient's spine 500. The illustrated example of thespine 500 includes the particular thoracic and lumbar vertebrae thattypically encompass a scoliotic curve, for example the curve of apatient with adolescent idiopathic scoliosis. The T3 through T12thoracic vertebrae, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512,respectively and the L1 through L3 vertebrae, 513, 514, 515 are depictedin FIG. 4, not in a severe scoliotic condition, but in a very slightresidual curve that represents a modest curve that has been partially orcompletely straightened during the implantation procedure.

Each vertebra is different from the other vertebra by its size andshape, with the upper vertebra generally being smaller than the lowervertebra. However, generally, the vertebrae have a similar structure andinclude a vertebral body 516, a spinous process 518, 520, laminae 526,transverse processes 521, 522 and pedicles 524. In this embodiment, thedistraction device 200 includes a distraction rod 206 which isadjustable (lengthwise) via a coupled adjustable portion 208. Thedistraction device 200 also includes a lower extension 209 which may bea short rod segment. The distraction device 200 is fixated to the spine500 via hooks 600, 601 at the upper end 202 of the distraction rod 206.Alternatively, a clamp may be secured around an adjacent rib (not shown)or rib facet. In still another alternative, a pedicle screw system maybe used.

Referring back to FIG. 4, the distraction device 200 is illustrated asbeing fixated to the spine 500 with a pedicle screw system 531, whichattaches directly to the lower extension 209. The distraction rod 206 isshown after it has been bent into a kyphotic curve, and the lowerextension is shown after it has been bent into a lordotic curve. Asexplained in more detail below. The adjustable portion 208 preferablycontains a magnetic assembly having a permanent magnet configured todrive a lead screw that, depending on the direction of rotation of theinternal magnet, will extend or retract the distraction rod 206 usingthe adjustable portion 208. Lengthening of the distraction rod 206, forexample, will impart a distraction force to the spine 500. Retractingthe distraction rod 206 will lower or remove the distraction force onthe spine 500, for example if too high a distraction force causes painor complications.

Because a scoliotic spine is also rotated (usually the center section isrotated to the right in AIS patients), the non-fusion embodimentpresented here allows de-rotation of the spine 500 to happen naturally,because there is no fixation at the middle portion of the distractiondevice 200.

In order to further facilitate this de-rotation, the distraction device200 may allow for free rotation at its ends. For example, the adjustableportion 208 may be coupled to the spine via an articulating joint. U.S.Patent Application Publication Nos. 2009-0112207 and 2010-0094302, bothof which are incorporated by reference, describe various articulatinginterfaces and joints that may be utilized to couple the adjustableportion 208 to the connecting rods or the like. These PublishedApplications further describe various distraction rod embodiments andmethods of use that may be used with inventions described herein.

As noted, the distraction rod 206 and the lower extension 209 may bebent by the user (or supplied pre-curved) with the typical shape of anormal saggital spine, but it should also be noted that the curve may beslightly different than standard scoliosis fusion instrumentation,because in the non-fusion embodiment described herein, the distractiondevice 200 is not usually flush with the spine but rather is placedeither subcutaneous or sub-fascial, and thus is not completely below theback muscles. In these less invasive methods, the only portions of thedistraction device 200 that are designed to be placed below the musclesare the hooks 600, 601 and the portion of the distraction rod 206immediately adjacent the hooks 600, 601, the pedicle screw system 531and the lower extension 209. Thus, FIG. 4 illustrates an embodiment inwhich the bulk of the hardware associated with the distraction device200 is placed over the muscle. It should be understood, however, that inalternative configurations, any other part of the entire implantableembodiment may be placed under the muscle (i.e., sub-muscular). Itshould be appreciated that a much smaller amount of muscle needs to bedissected during the procedure in comparison with current fusionprocedures. This will allow for a much shorter procedure, much lessblood loss, much quicker recovery, and less time in the hospital/lessrisk of infection.

By design, the distraction rod 206 is configured to be distracted fromthe adjustable portion, increasing the total device length via magneticadjustment. The preferred design for a distraction device 200, does notallow significant circumferential motion between the distraction rod 206and the adjustable portion 208. FIG. 5 illustrates a perspective view ofthe splined tip 220 of the distraction rod 206. The splined tip 220 isillustrated with four (4) protrusions 222 that interface with four (4)corresponding longitudinal grooves 224 (two pairs in symmetricopposition) formed inside a tubular housing 226 (illustrated in FIGS.6-7) of adjustable portion 208. The longitudinal grooves 224 may beformed by wire EDM machining or by broaching. While FIGS. 5-7 illustratean embodiment that uses four (4) protrusions 222 along with four (4)longitudinal grooves 224 there may be more or fewer. The tight toleranceof the splined tip 220 with the longitudinal grooves 224 keeps thedistraction rod 206 centered within the tubular housing 226. Inaddition, the combination of the splined tip 220 and correspondinggrooves 224 act as an anti-rotation feature that prevents thedistraction rod 206 from rotating relative to the tubular housing 226.This may be necessary to allow the distraction device 200 to be“rigidized” in the event the device is used in fusion applications,instead of the non-fusion applications described. For example, in afusion application, it is desired that the spine 500 not be able to flexor rotate much during the months that the fusion is taking place. Ineither the fusion applications or the non-fusion applications, theanti-rotation features are intended to limit inadvertent extensionand/or retraction of the distraction rod 206 resulting from, forinstance, patient movements. Additional details may be found in U.S.Patent Application Publication No. 2012-0035661, which is incorporatedherein by reference.

FIG. 8 is a view of a distraction device 300. Distraction device 300 hasdistraction rod 306 and adjustable portion 308. The distraction rod 306moves axially relative to the adjustable portion 308 and the device isidentical to the distraction device 200 described in FIG. 4. A lowerextension 309 extends from the adjustable portion 308 in a directionopposite the distraction rod 306. FIG. 9A is a longitudinal section ofthe distraction device 300 of FIG. 8 taken along the line 9A-9A, whileFIG. 9B is a cross-section of the same device taken along the line9B-9B. Distraction rod 306 contains an elongate recess 312 as seen inFIG. 9A containing a nut 314 at its end. Also at the end of thedistraction rod 306 are radial protrusions 322 which are configured toaxially slide within longitudinal grooves 324 formed within a tubularhousing 326 that forms part of the adjustable portion 308. O-ring gland330 includes a recess 332 which contains an o-ring 334, forming adynamic seal between the distraction rod 306 and the adjustable portion308. In addition, the internal diameter of the o-ring gland 330 may beformed of a lubricious material, such as PEEK or ultra high molecularweight polyethylene, creating a cylindrical bearing surface for enlargedportion 331 of distraction rod 306 to slide. This can increase thedistraction force of the distraction device 300 by minimizing the axialresistance. It can also minimize metal to metal particulate generation.Magnetic assembly 336 is rotatably held between a thrust bearing 350 anda radial bearing 346. The thrust bearing comprises two races with aplurality of balls in between. It is possible to have one of the racesdirectly formed within the internal end of the extension 309, but astandard thrust bearing is depicted in FIG. 9A. Magnetic assembly 336comprises a first cup 340 and a second cup 342 which adhesively containa radially-poled cylindrical magnet 354. The magnetic assembly 336 iscoupled to a lead screw 360 having external threads 362 which engage theinternal threads of the nut 314. The lead screw may be made of titaniumor titanium allow, while the nut may be made of aluminum-bronze and theymay both be coated with a biocompatible grease, such as Krytox, in orderto minimize resistance. The radial protrusions 322 may alternatively bemade as extensions of the nut 314, instead of as parts of thedistraction rod 306. The magnetic assembly 336 is coupled to the leadscrew 360 via a high strength pin 338. An expanded portion 305 oftubular housing 326 is configured to rotatably contain the magneticassembly 336. The tubular housing 326 is secured to the extension 309,for example, by a circumferential weld. As the magnetic assembly 336 isturned non-invasively by an externally applied rotating magnetic field,the lead screw 360 is forced to turn within the nut 314, causing thedistraction rod 306 to axially displace with relation to the adjustableportion 308.

Annularly contained between the magnetic assembly 336 and the expandedportion 305 of the tubular housing 326 is a cylindrical maintenancemember 303 made from a magnetically permeable material, such as 400series stainless steel. The cylindrical maintenance member 303 can beseen in isolation in FIG. 10. The cylindrical maintenance member 303 hastwo tabs 364 (one such tab is hidden from view in FIG. 10) radiallyopposed at one end. The tabs 364 are configured to engage into recessedareas 370 at the base of extension 309, within the interior of theadjustable portion 308. This allows the cylindrical maintenance member303 to remain non-rotatable or stationary with respect to the tubularhousing 326 and the extension 309. The cylindrical maintenance member303 comprises first and second side walls 372, 374, having first andsecond cut outs 366, 368 arrayed between them. When the distractiondevice 300 is not being adjusted, the magnetic poles 376, 378 of theradially-poled cylindrical magnet are magnetically attracted to thefirst and second side walls 372, 374 of the cylindrical maintenancemember 303 and tend to align with the first and second side walls 372,374. However, when the magnetic assembly 336 is forced to rotate due tothe effect of a sufficiently large rotating magnetic field on theradially-poled cylindrical magnet 354, the magnetic assembly 336overcomes the smaller attractions of the first and second side walls372, 374. FIG. 9B shows the magnetic assembly 336 actively being turnedin the direction or arrow 386. The poles 376, 378 of the radially-poledcylindrical magnet 354 are not shown as being aligned with the first andsecond side walls 372, 374. However, when the large rotating magneticfield is removed, the poles 376, 378 will align with the first andsecond side walls 372, 374. The magnetic attraction between the poles376, 378 and the first and second side walls 372, 374 serves to maintainthe specific amount of distraction length achieved in the distractiondevice 300, even as patient makes variable torsional, and compressivemotions (left, right extend, contract). The advantage of this design isthat the distraction device 300 is capable of being distracted, and ifit is over distracted, for example if it causes the patient pain ordiscomfort, it can be shortened. However, this free two-directionalcapability does not interfere with the stability of the distractionlength, because of the magnetic maintenance enabled by the first andsecond side walls 372, 374 of the cylindrical maintenance member 303.Representative dimensions include about 0.280 inches for the diameter ofthe radially-poled cylindrical magnet 354; about 0.305 inches for theouter diameter of both the first cup 340 and the second cup 342; about0.325 inches for the inner diameter of the cylindrical maintenancemember 303; and about 0.015 inches for the wall thickness of thecylindrical maintenance member 303.

FIG. 11 illustrates an external adjustment device 400 according to oneembodiment that includes two permanent magnets 402, 404 contained withinrespective covers 406. Each permanent magnet 402, 404 is rotatablewithin its respective cover 406 and provides a moving magnetic field. Amotor 408 is mechanically engaged to the permanent magnets 402, 404 viaa transmission (not shown) contained within a housing 410 of theexternal adjustment device 400

FIG. 12 illustrates another embodiment of a distraction device 700having a first distraction rod 701 and a second distraction rod 706, afirst adjustable portion 707, and a second adjustable portion 708.Distraction rods 701, 706 have respective ends 717, 719 configured forattachment to spine by known methods such as pedicle screws or hooks.Located in between the two adjustable portion 707 and 708 is anadjustable joint 711. A detail of adjustable joint 711 in FIG. 13 showsa first interfacing surface 713 and a second interfacing surface 715.Each interfacing surface 713, 715 contains several circumferentiallyarrayed teeth 721 as seen in FIG. 14, that allow the two interfacingsurfaces 713, 715 to engage with each other at a range of possibleangular orientations. The angle 723 can be made variable over a widerange of positive and negative angles (e.g., 90° or more), though inpractice, a much smaller range is needed. The chosen angle can be lockedby tightening a locking member 725 such as a securing screw. The angle723 may, for example, be chosen to match the current kyphosis (sagittalplane) of a patient, or the desired thoracic kyphosis through treatment.For example, an angle within the normal range of 20° to 50° may be used.Alternatively, if the patient is hyperkyphotic or hypokyphotic, theparticular angle of kyphosis, outside the normal range, may be chosen.Each adjustable portion 707, 708 may be independently lengthened, usingthe magnetic lengthening technique described herein. It may be desirableto lengthen one of the sides of the distraction device 700 and not theother. For instance, first distraction rod 701 may be extended from thefirst adjustable portion 707 while the second distraction rode 706 maynot move relative to the second adjustable portion 708. Alternatively,by adjusting both sides (707, 708) equally, the apex thoracic kyphosismay be maintained at the same level of the spine. By lengthening theside towards the head more than the side towards the feet, the apex ofthe thoracic kyphosis may be moved towards a lower area of the spine. Bylengthening the side towards the feet more than the side towards thehead, the apex of the thoracic kyphosis may be moved towards an upperarea of the spine. Furthermore, by lengthening the side towards the headand shortening the side towards the feet, the apex of the thoracickyphosis may be more drastically moved towards a lower area of thespine, and by lengthening the side towards the feet and shortening theside towards the head, the apex of the thoracic kyphosis may be moredrastically moved towards an upper area of the spine.

The distraction device 700 of FIG. 12 contains other features that makeit appropriate for use as a temporary rod, in gradually correcting asagittal (hyperkyphosis, hypokyphosis) or coronal (scoliosis) deformityin a patient with a mature spine. The two adjustable portions 707, 708allow 70 mm each of axial lengthening and so together allow for a totalof 140 mm of lengthening. If the spine were to be significantlydistracted manually (without the magnetic actuation) at the implantsurgery, then this amount of total lengthening would probably not beneeded. In growing patients, the magnetic actuation is intended tocorrespond with growth. However, in a no longer growing patient, andparticularly in a patient whose treatment regime would benefit fromgradual distraction, the axial lengthening is intended to partially orsubstantially straighten a curved spine, would often require a totaldistraction length as long as 140 mm, and even as high as 240 mm in alarge patient with a severe deformity (greater than 90°). In addition tothe length required in the axial distraction to make a curve spinestraight, there will actually be additional length that will often needto applied, in order to overstrain and permanently stretch ligaments ofthe vertebrae. In some cases, these ligaments may require as much as 30%or even 50% additional strain in order to permanently change theirlength as desired. This is analogous to the stretching done on ligamentsand other soft tissue in joint splinting applications. The mechanism forligament stretching can be stress relaxation and viscoelasticity of thesoft tissue and even some micro cracking or “neck down.” The adjustableportions 707, 708 in the distraction device 700 also have planetarygearing 727 disposed between the magnetic assembly 736 and the leadscrew 760 (illustrated only in adjustable portion 707 in FIG. 12). Thegearing 727 allows for a significantly higher distraction force to beplaced on the spine. In the mature spine patients, the spine is oftenstiffer, and requires significantly more force than when distracting animmature spine. Depending on the patient, forces as high as 112 pounds(500 Newton) or higher may be required to significantly cause stretchingof spinal ligament groups. Gear ratios of 4:1, 16:1 and 64:1, forexample, from one, two, or three sets of planetary gears, can beincorporated in order to multiply the deliverable distraction force byclose to four, sixteen or sixty four times. In an assembly with three4:1 planetary gear sets, with a total gear ratio of 64:1, the magneticassembly would make sixty four rotations for every one rotation of thelead screw. In keeping with the gradual distraction treatmentmethodology, the distraction device 700 may be positioned in patientduring implantation surgery so that the angle is oriented in a planewhich is between the sagittal and coronal plane, allowing it to in partmatch the contours of the patients current or desired kyphotic curve,but also, to fit on a spine that has a residual scoliotic curve.

Turning now to FIG. 15, another embodiment of a distraction device 800having a single, central distraction rod 806 is depicted. Two adjustableportions 807, 808 are coupled to the commonly shared distraction rod806. Adjustable portion 807 is coupled to a first end 829 of thedistraction rod 806 while adjustable portion 808 is coupled to theopposite end 833 of distraction rod 806. More specifically, adjustableportion 807 includes a rotatable magnetic assembly 811 that is coupledto a lead screw 813 that interfaces with a threaded portion locatedinside the first end 829 of the distraction rod 806. For example, asexplained in other embodiments, a nut having internal threads may bedisposed in a recess of the first end 829 of the distraction rod 806 andmay interface with the lead screw 813. Likewise, adjustable portion 808includes a rotatable magnetic assembly 815 that is coupled to a leadscrew 817 that interfaces with a threaded portion (e.g., threaded nut asdescribed above) located inside the second end 833 of the distractionrod 806. As in FIG. 14, ends 817, 819 are configured for attachment tospine by known methods such as pedicle screws or hooks. However, indistraction device 800, ends 817, 819 extend from adjustable portions807, 808, as opposed to extending from a distraction rod. Thedistraction rod 806 may be supplied to the surgeon with a typicalsagittal curve, for example a typical thoracic kyphosis. Alternatively,the distraction rod 806 may be supplied straight, and may be bent to adesired curve by the surgeon, using a French bender or in situ benders.The distraction rod 806 may also be supplied to the surgeon in a firstcurved shape, and may be modified by the surgeon into a second curvedshape. An advantage to both the distraction device 700 of FIG. 12 andthe distraction device 800 of FIG. 15 is that the total length of thenon-bendable or non-angulating portions (essentially the adjustableportions 707,708 or 807,808) can be shorter. For example, if thedistraction device 800 of FIG. 15 had a single 90 mm long adjustableportion capable of lengthening 48 mm it might be considered to be toolong and straight at the adjustable portion for a certain group ofpatient anatomies. However, if this device were instead made with twoadjustable portions, for example 66 mm long each, with the curved orbendable distraction rod 806 in between, and each adjustable portionwere capable of 24 mm of lengthening, the device would more acceptablycontour to these patients' anatomies. In use, instead of lengthening thesingle actuator 4 mm, for example, the physician might lengthen eachactuator 2 mm, for 4 mm total.

Distraction device 900 in FIG. 16 has a single adjustable portion 908which is configured in a permanently curved or angled shape.Alternatively, this adjustable portion 908 may actually be made of abendable tube. The permanently curved or angled adjustable portion 908comprises a tubular housing 926 and an expanded portion 905. In theembodiment specifically depicted, an intermediate tubular section 935 iswelded to both the tubular housing 926 and the expanded portion 905.Distraction rod 906 actuates axially within adjustable portion 908.Extension 909 is coupled to adjustable portion 908 at the other end. Thedevice may be supplied with angle 937 of between 3° and 35°, and moreparticularly, with an angle 937 of about 10°. This angle again,depending upon the use of the device, may be oriented on the patientcompletely within the sagittal plane, or between the sagittal andcoronal planes. As seen in FIG. 16, the rotatable magnetic assembly 936is disposed in the tubular section 935 and is coupled to a lead screw960 via a universal joint 941 (described in more detail below). The leadscrew 960 interfaces with the distraction rod 906, for example, athreaded nut or the like as described elsewhere herein. Rotation of themagnetic assembly 936 causes lead screw 960 to rotate which thentranslations into axial, telescopic movement of the distraction rod 906relative to the housing 926.

FIG. 17A illustrates an internal assembly 939 of the distraction device900 of FIG. 16. Magnetic assembly 936 comprises first cup 940 and secondcup 942, which adhesively contain a radially-poled cylindrical magnet954. The magnetic assembly 936 is configured for rotation via a radialbearing 946 at one end and a thrust bearing (not shown) at the otherend. The radial bearing 946 is placed annularly around a smallerdiameter extension of the first cup 940. The magnetic assembly 936 iscoupled to a lead screw 960 by a universal joint 941, which isconstructed as follows. Extending from the smaller diameter extension ofthe first cup 940 are two tabs 943, 945. Also extending from the end ofthe lead screw 960 are two tabs 947, 949. Each of the four tabs 943,945, 947, 949 has a through hole 951. A cross 953, as best seen in FIG.17B, consisting of four ends 955 separated by 90° each couples the tabs943, 945 of the first cup 940 to the tabs 947, 949 of the lead screw960, the ends 955 each passing through one of the through holes 951 sothat the magnetic assembly 936 and the lead screw 960 remain secured toeach other, while the ends 955 are free to angularly displace within thethrough holes 951. This allows a torque placed on the magnetic assembly936 to be transferred with very good efficiency to the lead screw 360,even though they are not both oriented along the same axis.

While FIG. 17A illustrates a magnetic assembly 936 that includes amagnet 954, in other alterative embodiments, the magnetically assemblydoes not need to include a magnet. Instead, as seen in FIG. 17C, amagnetic assembly 975 may include circumferentially arrayed magneticallypermeable elements 977, for example 400 series stainless steelcomponents. These circumferentially arrayed magnetically permeableelements 977 can be arrayed in such a way so that they are alsomagnetically drivable by a rotating magnetic field (e.g., arrayed at oneor more circumferential locations about a common axis of rotation). Amagnetic assembly 975 may even include only one magnetically permeableelement 977 if, for example, either two external adjustment devices 400are used; a first external adjustment device 400 located on a first sideof the patient and a second external adjustment device 400 located on asecond side of the patient, so that the first external adjustment device400 turns the magnetic assembly 975 over an arc of 180° and the secondexternal adjustment device 400 turns the magnetic assembly 975 overanother 180°. Alternatively, a single external adjustment device 400 maybe configured that turns at least one magnet located on a first side ofthe patient while also turning a second magnet located on a second sideof the patient. As still another alternative, the magnetic assembly maybe replaced by a motor which is configured to drive the screw. The motormay be powered by an implantable battery, or may be powered (andcontrolled) via an inductive coupling, for example a coupling thatallows a capacitor to be charged non-invasively.

FIGS. 18-21 illustrate a manual distraction tester 1100 configured forplacement over a distraction device 1000 having a distraction rod 1006,an adjustable portion 1008, and expanded portion 1005 and an extension1009. The use of this manual distraction tester removes the need to usethe actual external adjustment device 400 to test the distraction device1000 during the implantation surgery. The manual distraction tester 1100has a body portion with a hollow cylindrical cavity 1057 (seen in FIG.18) there through which is sized for placing over the expanded portion1005 of the distraction device 1000. For example, if the expandedportion 1005 has a diameter of 10.5 mm, the hollow cylindrical cavity1057 may have a diameter of 11.0 mm for clearance. The manualdistraction tester 1100 has a minimally magnetic circumferential portion1059, and a maximally magnetic circumferential portion 1061. Theminimally magnetic circumferential portion 1059 and the maximallymagnetic circumferential portion 1061 are spaced apart from one anotherabout the periphery of the body of the manual distraction tester 1100.The maximally magnetic circumferential portion 1061 is configured toattract one of the poles of the implanted magnet of the distractiondevice, while the minimally magnetic circumferential portion 1059 isconfigured to either not attract a magnetic pole at all, or to attract apole significantly less than the maximally magnetic circumferentialportion 1061, so that the attraction of the pole by the maximallymagnetic circumferential portion 1061 dominates.

As illustrated, the entire body of the manual distraction tester 1100 ismonolithic and configured from a single material, for example 420stainless steel, although other materials having magnetic permeabilitymay be used. Thought the minimally magnetic circumferential portion 1059has some attraction to magnet poles, the significantly larger mass ofthe maximally magnetic circumferential portion 1061 dominates. One wayto achieve the difference in magnetic attraction between the twocircumferential portions, if the manual distraction tester 1100 is madeentirely from 420 stainless steel, is to make, for example the axialthickness of the minimally magnetic circumferential portion 1059 small(for example 2.5 mm) and the axial thickness of the maximally magneticcircumferential portion comparatively large (for example 19 mm). Themanual distraction tester 1100 is axially slid onto the distractiondevice 1000 in the direction of the arrow 1065 in FIG. 19, and themaximally magnetic circumferential portion 1061 immediately orients witha pole of the radially-poled cylindrical magnet (not shown) within theexpanded portion 1005 of the distraction device 1000. Alternatively, themanual distraction tester 1100 may be placed onto the distraction device1000 from the other end. The manual distraction tester has knurls 1063which aid in rotating it by hand.

The manual distraction tester 1100 is turned in a first direction 1069,magnetically causing the radially-poled cylindrical magnet to turn andin turn to cause lengthening of the distraction device 1000. A mark 1071on the distraction rod 1006 can easily be seen moving in relation to anend 1073 of the adjustable portion 1008 of the distraction device 1000.FIG. 20 shows the manual distraction tester 1100 being turned in a firstdirection 1069 and the mark 1071 displaced axially to indicate thatlengthening is correctly occurring, and that functionality has beenconfirmed. FIG. 21 shows the manual distraction tester 1100 then beingturned in a second direction 1067, causing the distraction device 1000to shorten. The mark 1071 has returned to its original position. Themark may be placed on the distraction rod 1006 by laser markingtechnique, printing or equivalent methods. A face 1075 of the manualdistraction tester 1100 has markings which show, for example, thecorrect orientation at which the manual distraction tester 1100 shouldbe placed, for example an arrow pointing cephalad (towards the head ofthe patient), the rotation to turn in order to lengthen the distractiondevice 1000, and the direction to turn in order to shorten thedistraction device 1000. These may also be laser marked or printed.Alternative to the construction shown, it is also contemplated to makethe manual distraction tester from a non-magnetic frame (such as nylon,PEEK, titanium, ABS, or a polymer) with a large piece of magneticmaterial (such as 420 stainless steel) attached at the maximallymagnetic side 1061. The manual distraction tester 1100 may be coated onthe hollow cylindrical cavity 1057 surface, to aid in its ability tosmoothly slide or turn, without scratching the distraction device 1000.

A distraction rod 1206 is shown in FIGS. 22-24 which includes a nut 1214having an internal thread 1277. Nut 1214 is axially maintained withindistraction rod 1206 by flange 1279 which is within cavity 1281. Bothflange 1279 and cavity 1281 may optionally extend 360° around nut 1214and distraction rod 1206 respectively. Distraction rod 1206 has aplurality of protrusions 1222 a (e.g., four) which are configured toslide axially within longitudinal grooves of the housing holding therotatable magnetic assembly (e.g., longitudinal grooves 224 of FIG. 6 orlongitudinal grooves 324 of FIG. 9A). Nut 1214 also has four protrusions1222 b which are also configured to slide axially within longitudinalgrooves 224, 324. Internal thread 1277 is configured to interface withexternal thread 362 of lead screw 360. As seen in FIG. 24, at therespective ends of internal thread 1277 is a first collar 1283 and asecond collar 1285. The first and second collars 1283, 1285 are disposedon opposing sides of the internal thread 1277 of the nut 1214. The innerdiameter of first and second collars 1283, 1285 is approximately equalto the major diameter of the internal thread 1277. When external thread362 of lead screw 360 is engaged with internal thread 1277 of nut 1214and the patient is not being lengthened, the first and second collars1283, 1285 serve to minimize the ability of the nut 1214 to “walk” alonglead screw 360 when the patient moves (either compressing, tractioningor torsioning rod). However, lead screw 360 and nut 1214 do not dig intoeach other, because nut 1214 retains some free movement because of gap1287 between the outer diameter 1289 of nut 1214 and inner bore diameter1291 of distraction rod 1206.

When adjusting the length of the distraction device, the lead screw 360turns within nut 1214 because protrusions 1222 a of distraction rod 1206and protrusions 1222 b of nut 1214 are held within longitudinal grooves224, 324 of the housing and so they remain rotationally static withrespect to adjustable portion 308, while allowing distraction rod 1206to axially adjust in relation to adjustable portion 308. This collarednut 1214 allows a stability of the distraction length of the distractiondevice that precludes the need for the cylindrical maintenance member303 of FIGS. 9A, 9B, and 10. In less demanding applications, a simplerversion of the nut 1214 may be used, wherein the nut 1214 has the innerthread 1277, first collar 1283 and second collar 1285, but ispermanently bonded (with epoxy for example) within the inner borediameter 1291 of distraction rod 1206. In such an embodiment, there isno gap 1287.

While embodiments have been shown and described, various modificationsmay be made without departing from the scope of the inventive conceptsdisclosed herein. The embodiments have application in many other medicalconditions, including lengthening of bones by intramedullary placeddistraction devices or by distracting plates placed on the exterior ofbones. The invention(s), therefore, should not be limited, except to thefollowing claims, and their equivalents.

What is claimed is:
 1. A distraction system comprising: a first distraction device comprising a first adjustable portion and a first distraction rod configured to telescope within the first adjustable portion, the first adjustable portion having contained therein a first rotatable magnetic assembly mechanically coupled to a first screw configured to axially telescope the first distraction rod; a second distraction device comprising a second adjustable portion and a second distraction rod configured to telescope within the second adjustable portion, the second adjustable portion having contained therein a second rotatable magnetic assembly mechanically coupled to a second screw configured to axially telescope the second distraction rod; and an adjustable joint connecting one end of the first adjustable portion to one end of the second adjustable portion.
 2. The distraction system of claim 1, wherein the adjustable joint comprises a first interfacing surface coupled to the first adjustable portion and a second interfacing surface coupled to the second adjustable portion, and a locking member configured to secure the first interfacing surface to the second interfacing surface.
 3. The distraction system of claim 2, wherein the locking member comprises a screw.
 4. The distraction system of claim 2, wherein the first interfacing surface and the second interfacing surface comprise circumferentially arrayed teeth.
 5. The distraction system of claim 1, wherein the adjustable joint comprises a locking pivot joint.
 6. A distraction system comprising: a first distraction device comprising a first adjustable portion having contained therein a first rotatable magnetic assembly; a second distraction device comprising a second adjustable portion having contained therein a second rotatable magnetic assembly; and a common distraction rod having first and second opposing ends, wherein a first end of the common distraction rod is mechanically coupled to the first rotatable magnetic assembly and wherein a second end of the common distraction rod is mechanically coupled to the second rotatable magnetic assembly.
 7. The distraction system of claim 6, wherein the common distraction rod is bendable.
 8. The distraction system of claim 6, wherein the common distraction rod is straight.
 9. The distraction system of claim 6, wherein the common distraction rod is curved.
 10. A distraction system comprising: an adjustable portion having contained therein a rotatable magnetic assembly, the adjustable portion being at least one of curved or angled; and a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion.
 11. The distraction system of claim 10, wherein the curve or angle of the adjustable portion defines an angle within the range of about 3° and 35°.
 12. The distraction system of claim 11, wherein the adjustable portion comprises a bendable tube.
 13. The distraction system of claim 10, further comprising a universal joint coupling the screw to the rotatable magnetic assembly.
 14. A distraction system comprising: an adjustable portion having contained therein a rotatable magnetic assembly; a screw operatively coupled to the rotatable magnetic assembly; and a distraction rod having a recess formed therein, the recess containing a nut having internal threads, the nut comprising first and second collared ends disposed on either side of the internal threads, wherein the screw interfaces with the internal threads of the nut and wherein rotation of the rotatable magnetic assembly effectuates telescopic movement of the distraction rod relative to the adjustable portion.
 15. The distraction system of claim 14, wherein the nut is bonded directly to the distraction rod.
 16. The distraction system of claim 14, wherein the adjustable portion comprises a housing having a plurality of longitudinal grooves disposed along an inner surface thereof and wherein the nut comprises a plurality of protrusions configured to fit within the plurality of longitudinal grooves.
 17. The distraction system of 14, wherein the distraction rod comprises a cavity disposed along the recess and the nut comprises a flange dimensioned to fit within the cavity.
 18. The distraction system of claim 14, further comprising a gap formed between an outer diameter of the nut and an inner diameter of the recess.
 19. A distraction system comprising: an adjustable portion having contained therein a rotatable magnetic assembly a distraction rod mechanically coupled to the rotatable magnetic assembly via a screw and configured for telescopic movement relative to the adjustable portion; and a distraction tester comprising a body having a cylindrical cavity passing through the body, wherein the distraction tester has a first circumferential portion of the body that has a higher mass of a magnetically permeable material as compared to a second circumferential portion of the body spaced apart from the first circumferential portion.
 20. The distraction device of claim 19, wherein the first circumferential portion of the body is substantially thicker than the second circumferential portion of the body.
 21. The distraction device of claim 1, wherein the first and second rotatable magnetic assemblies comprise at least one of a magnet or circumferentially arrayed magnetically permeable elements.
 22. The distraction device of claim 6, wherein the first and second rotatable magnetic assemblies comprise at least one of a magnet or circumferentially arrayed magnetically permeable elements.
 23. The distraction device of claim 10, wherein the rotatable magnetic assembly comprises at least one of a magnet or circumferentially arrayed magnetically permeable elements.
 24. The distraction device of claim 14, wherein the rotatable magnetic assembly comprises at least one of a magnet or circumferentially arrayed magnetically permeable elements. 